/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.concurrent;

import java.util.concurrent.Callable;
import java.util.concurrent.Executor;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

/**
 * Extension for the {@link Executor} interface which is enriched by method for scheduling tasks
 * in the future.
 */
public interface ScheduledExecutor extends Executor {

	/**
	 * Executes the given command after the given delay.
	 *
	 * @param command the task to execute in the future
	 * @param delay the time from now to delay the execution
	 * @param unit the time unit of the delay parameter
	 * @return a ScheduledFuture representing the completion of the scheduled task
	 */
	ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit);

	/**
	 * Executes the given callable after the given delay. The result of the callable is returned
	 * as a {@link ScheduledFuture}.
	 *
	 * @param callable the callable to execute
	 * @param delay the time from now to delay the execution
	 * @param unit the time unit of the delay parameter
	 * @param <V> result type of the callable
	 * @return a ScheduledFuture which holds the future value of the given callable
	 */
	<V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit);

	/**
	 * Executes the given command periodically. The first execution is started after the
	 * {@code initialDelay}, the second execution is started after {@code initialDelay + period},
	 * the third after {@code initialDelay + 2*period} and so on.
	 * The task is executed until either an execution fails, or the returned {@link ScheduledFuture}
	 * is cancelled.
	 *
	 * @param command the task to be executed periodically
	 * @param initialDelay the time from now until the first execution is triggered
	 * @param period the time after which the next execution is triggered
	 * @param unit the time unit of the delay and period parameter
	 * @return a ScheduledFuture representing the periodic task. This future never completes
	 * unless an execution of the given task fails or if the future is cancelled
	 */
	ScheduledFuture<?> scheduleAtFixedRate(
		Runnable command,
		long initialDelay,
		long period,
		TimeUnit unit);

	/**
	 * Executed the given command repeatedly with the given delay between the end of an execution
	 * and the start of the next execution.
	 * The task is executed repeatedly until either an exception occurs or if the returned
	 * {@link ScheduledFuture} is cancelled.
	 *
	 * @param command the task to execute repeatedly
	 * @param initialDelay the time from now until the first execution is triggered
	 * @param delay the time between the end of the current and the start of the next execution
	 * @param unit the time unit of the initial delay and the delay parameter
	 * @return a ScheduledFuture representing the repeatedly executed task. This future never
	 * completes unless the execution of the given task fails or if the future is cancelled
	 */
	ScheduledFuture<?> scheduleWithFixedDelay(
		Runnable command,
		long initialDelay,
		long delay,
		TimeUnit unit);
}
